1. Field of the Invention
The present invention relates to a piston valve, and more particularly, to a piston valve of a shock absorber in which a frequency sensitive valve unit is installed inside of a pressure sensitive main valve unit to reduce the entire length of the piston valve.
2. Description of the Prior Art
In general, a vehicle continuously receives vibration or a shock from a road surface through the wheels during driving. Thus, a shock absorbing device is provided between the vehicle body and the vehicle axle so as to prevent the shock or vibration from being directly transferred to the vehicle body, thereby improving ride comfort. In addition, the shock absorbing device suppresses the irregular vibration of the vehicle body, so as to enhance the driving stability.
A suspension system, which is a general name of a connection device between a vehicle axle and a vehicle body including the shock absorbing device as described above, includes a chassis spring configured to relieve shock, a shock absorber configured to control the free vibration of the chassis spring so as to improve ride comfort, a stabilizer configured to prevent rolling, a rubber bushing, and a control arm.
In the suspension system, especially, the shock absorber serves to suppress and attenuate vibration from the road surface and is mounted between the vehicle body or a frame and a wheel. In particular, the shock absorber absorbs the vibration energy of the vehicle body in the vertical direction, so as to suppress vibration, improve the ride comfort, and protect cargo on board. In addition, the shock absorber increases the service life of the vehicle by reducing dynamic stresses at each portion of the vehicle body and secures tires' road holding by suppressing the motion of a mass below the spring. Furthermore, the shock absorber improves the motional performance of the vehicle by suppressing change in the vehicle's posture caused by an inertial force.
Accordingly, the ride comfort and handling stability of the vehicle may be suitably adjusted according to the attenuation force characteristic of the shock absorber. That is, during the normal driving of the vehicle, it may be needed to reduce the attenuation force so as to improve ride comfort. Further, when quickly turning the vehicle or during the high-speed driving of the vehicle, it may be needed to increase the attenuation force so as to enhance the handling stability.
FIG. 1 illustrates a conventional shock absorber.
As illustrated in FIG. 1, the shock absorber 1 includes a cylinder 2 filled with hydraulic fluid, a piston rod 3 of which one end is positioned inside the cylinder 2 and the other end extends to the outside of the cylinder 2, and a piston valve 4 mounted at the one end of the piston rod 3 to reciprocate in the cylinder 2.
The cylinder 2 may include an inner tube 2a and an outer tube 2b, and a base valve 5 is installed at the lower end of the cylinder 2 to face the piston valve 4.
The inside of the cylinder 2 is divided into an extension chamber C1 and a compression chamber C2 by the piston valve 4. When the piston valve 4 reciprocates up and down within the cylinder 2, the hydraulic fluid flows from the extension chamber C1 to the compression chamber C2 or from the compression chamber C2 to the extension chamber C1 through an orifice (not shown) formed in the piston valve 4, thereby generating an attenuation force.
The conventional shock absorber 1 configured as described above is adapted to generate the attenuation force using a pressure difference between the extension chamber C1 and the compression chamber C2 which occurs according to the rectilinear reciprocation of the piston rod 3 connected to the vehicle body. Thus, when the moving stroke of the piston rod 3 is large or at a low frequency shock region, a proper attenuation force is generated to smoothly absorb vibration. However, when the moving stroke of the piston rod 3 is small or at a high frequency shock region, a proper attenuation force may not be obtained.
Thus, a frequency sensitive shock absorber has been developed in which the attenuation force may be adjusted according to the variation of shock frequency as well as the shock input speed. As an example of such a frequency sensitivity shock absorber, FIG. 2 illustrates a shock absorber for a vehicle disclosed in Korean Patent No. 10-0489417 (Patent Document 1).
The shock absorber 20 for a vehicle illustrated in FIG. 2 includes: a first communication bore 32 formed in the lower portion of a piston rod 31 so as to allow an extension chamber 23 and a compression chamber 24 to communicate with each other within a cylindrical tube 22; a valve body 33 including a first body 33a and a second body 33b which are coupled to each other at the lower end of the piston rod 31 to form a space 34 inside of the first body 33a and the second body 33b, each of the first body 33a and the second body 33b having a second communication bore 35, which is formed through the first body 33a and the second body 33b and at the top and bottom of the space 34, so as to allow the first communication bore 32 and the compression chamber 24 to communicate with each other; and a balancing weight 36 installed within the space 34 of the valve body 33 to be movable up and down by a pair of springs 37 and 38 so as to open or close the second communication bore 35.
Thus, when the moving stroke of the piston rod 31 is small or a high frequency shock is applied,
the fluid within the extension chamber 23 and the compression chamber 24 is circulated within the compression chamber 24 and the extension chamber 23 through the first communication bore 32 formed through the piston rod 31 and the second communication bore 35 formed through the valve body 33 to absorb the shock, even if a disk 28 for opening or closing fluid channels 26 and 27 formed in the piston valve 25 does not operate.
However, in the above-described frequency sensitive shock absorber 20, a frequency sensitive valve is separately installed below the conventional pressure sensitive piston valve 25 to be spaced apart from and in series to the pressure sensitive piston valve 25. Thus, the entire length of the shock absorber 20 increases. In addition, the degree of design freedom of the shock absorber 20 may be limited due to the increase of manufacturing time and costs and the problem of installation space.
In addition, when a low frequency and high amplitude shock occurs in a moment, the shock should be sufficiently absorbed. However, since the shock absorber 20 illustrated in FIG. 2 relies only on the operation of the conventional piston valve 25, such a momentary low frequency and high amplitude shock cannot be sufficiently relieved.
Furthermore, there is a problem in that, when the balancing weight 36 is moved up and down due to a high frequency vibration, friction sounds may be generated due to the contact between the windings of the springs 37 and 38.